Marine antifoulant coating

ABSTRACT

A protective coating applied to the underwater portion of a marine vessel operable to inhibit the growth of marine foulants. The coating comprises a polymer, a marine biocide, a preservative, and optionally an antimicrobial agent. In certain embodiments, the marine biocide, preservative, and optional antimicrobial agent are chemically bonded with the polymer thereby significantly reducing the ability of the biocide, preservative, and antimicrobial agent to leach from the coating into the surrounding environment.

RELATED APPLICATIONS

The present application is a divisional patent application and claimspriority benefit, with regard to all common subject matter, toearlier-filed U.S. non-provisional patent application entitled “MARINEANTIFOULANT COATING”, Ser. No. 11/778,193, filed Jul. 16, 2007. Theidentified earlier-filed patent application is incorporated in itsentirety into the present application by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

Embodiments of the present invention relate to a coating that is appliedto a surface. More particularly, embodiments of the present inventionrelate to a protective coating that is applied to the underwater portionof a marine vessel so as to inhibit the growth of marine foulants.

2. Description of the Related Art

Marine vessels that reside in a water environment over certain lengthsof time can accumulate biological growth, known as foulants, on thosesurfaces that are in contact with the water. Diverse species of hard andsoft fouling organisms, such as barnacles, zebra mussels, algae, andslime, form colonies on the underwater surfaces of the vessel,particularly when a vessel is docked, because each requires a permanentanchorage in order to mature and reproduce. Marine growth fouling addsweight to a ship, increases the amount of fuel consumed, and reduces itsspeed.

Historically, to combat the growth of marine foulants, the underwatersurfaces of ships have been coated with antifoulant paints, which ofteninclude toxic materials to inhibit biological growth. The antifoulantpaints may degrade and break down over time, releasing the toxicmaterials from the marine vessel into the surrounding water. These toxicmaterials may include volatile organic compounds (VOCs) and hazardousair pollutants (HAPs). The International Maritime Organization and theUnited States Environmental Protection Agency have enacted regulationsand standards that restrict the emission of VOCs and HAPs fromantifoulant paints. The decomposition and break down of the antifoulantpaint results in reduced efficacy of the protection afforded by theantifoulants, thereby requiring reapplication of the paint in arelatively short time. Thus, a coating material is required that can beapplied to the underwater surfaces of a marine vessel which repels thegrowth of fouling organisms on such surfaces and has an extendedlifetime without releasing significant amounts of toxic materials intothe environment.

SUMMARY OF THE INVENTION

Embodiments of the present invention solve the above-mentioned problemsand provide a distinct advance in the art of coatings applied to asurface. More particularly, embodiments of the invention provide aprotective coating applied to the underwater portion of a marine vesseloperable to inhibit the growth of marine foulants. Furthermore, thecoating does not degrade significantly over time which leads to a longereffective lifetime and a greatly reduced emission of toxic materials ascompared with conventional antifoulant paints.

Various embodiments of the present invention provide an antifoulantcoating comprising a polymer that adheres to a surface of a marinevessel that contacts water, a preservative and a marine biocide. Incertain embodiments, the preservative and marine biocide are chemicallybonded to the polymer so as to prevent leaching of the preservativeand/or biocide into the surrounding marine environment.

In another embodiment, a method of forming a marine antifoulant coatingis provided. The method comprises forming a mixture comprising particlesof a polymer, a marine biocide, and a preservative. The mixture isheated to a temperature above the glass transition temperature of thepolymer thereby forming a flowable mixture comprising the polymer havingparticles of the biocide and preservative dispersed therein. A variableelectric field is applied to the heated mixture to alter the orientationof the polymer and the particles of biocide and preservative relative toeach other.

In yet another embodiment, a method of applying a marine antifoulantcoating to a surface of a marine vessel is provided. The methodcomprises injecting a heated blended mixture comprising a polymer, amarine biocide, and a preservative into a plasma stream. The plasmastream and heated blended mixture are enshrouded with a shielding gas toprevent contamination of the heated blended mixture. The plasma streamand heated blended mixture are directed onto the marine vessel surfacewhereby the heated blended mixture becomes adhered to the surface.

This summary is provided to introduce a selection of concepts in asimplified form that are further described below in the detaileddescription. This summary is not intended to identify key features oressential features of the claimed subject matter, nor is it intended tobe used to limit the scope of the claimed subject matter.

Other aspects and advantages of the present invention will be apparentfrom the following detailed description of the preferred embodiments.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The embodiments illustrated in the following detailed description areintended to describe aspects of the invention in sufficient detail toenable those skilled in the art to practice the invention. Otherembodiments can be utilized and changes can be made without departingfrom the scope of the present invention. The following detaileddescription is, therefore, not to be taken in a limiting sense. Thescope of the present invention is defined only by the appended claims,along with the full scope of equivalents to which such claims areentitled.

The coating is generally operable to inhibit the growth of marinefouling organisms on the underwater portion of a marine vessel byrepelling the marine organisms when they contact the coating. In variousembodiments, the coating also reduces the ability of fouling organismsto adhere to the coated marine vessel surface. Some growth of organismson the coating may occur, particularly when the vessel is idle, but theorganisms detach and slough off as the vessel begins moving through thewater. The coating prevents the fouling organisms from strongly adheringto the marine vessel so that the motion of water across the surface ofthe coating serves as a rinsing action to clean the surface of anyfouling growth.

In various embodiments, the coating comprises a polymer, a marinebiocide, and a preservative. In other embodiments, the coating furthercomprises an antimicrobial agent.

The polymer component serves as a foundation for the antifoulant coatingin which the other components of the coating are dispersed. Withoutdesiring to be bound by any particular theory, it is believed that thepolymer functions as a matrix to which the other components arechemically bonded. Furthermore, it is believed that the preservative andmarine biocide may be covalently bonded to the polymer, althoughcertainly it is within the scope of the invention for these bonds to beof an ionic nature as well.

In any event, the polymer binds the preservative and marine biocide inthe coating and helps to retain them against the target surface, such asthe hull of a ship. The polymer may be a polyamide including varioustypes of nylon such as nylon 11 or nylon 12, available under the nameVESTOSINT® by Degussa of Dusseldorf, Germany. The polymer may also be animpact resistant powder coating resin, such as SURLYN® (ionomer),ABCITE® X60 or ABCITE® X70 by DuPont of Wilmington, Delaware. In variousembodiments, the listed polymers may be polar in nature. Generally, thepolymer presents the characteristics of increased adhesion to varioussubstrates (particularly metal), high impact resistance, and highresistance to degradation.

In various embodiments, the polymer may also include a fluoropolymer,such as polytetrafluoroethylene (PTFE), perfluoroalkoxy polymer resin(PFA), polyethylenetetrafluoroethylene (ETFE), or polyvinylidenefluoride (PVDF), or powdered silicone in combination with any of thepolymers listed above. It is possible that the listed components arenon-polar. These additive components are typically included to decreasethe coefficient of friction of the antifoulant coating and wouldprimarily be used in situations where the vessel is faster moving,thereby benefiting from a decreased drag on the ship.

Generally, the polymer is supplied in a powder form having averageparticle sizes ranging from about 20 microns (μm) to about 80 μm. Inother embodiments, the polymer may be supplied in a nano-sized formwherein the average particle size is between about 25 nanometers (nm) toabout 40 nm.

The polymer typically presents a glass transition temperature that islower than the melting point of the other components included in theantifoulant coating. Thus, the polymer enters the glass transition phaseand bonds with the other components before the other components begin tomelt. Thus, the marine biocide and preservative are present as discreteparticles dispersed within the polymer matrix. Additionally, the polymeris compatible with the target surface so as to adhere strongly theretoonce applied. The glass transition temperature of the polymer may bewithin the range of about 176° F. to about 248° F.

The marine biocide generally comprises a metal component such as copperor silver. Biocides containing metal components are well known in theart. The biocide may be supplied as copper oxide (also known as cuprousoxide or Cu₂O), copper and silver coated hollow micro spheres, silverand copper-clad mica flake, or AgION™ antimicrobial by Agion ofWakefield, Mass. Copper oxide is widely used and is available in severalgrades, Red Copper 97, Premium grade Purple 97N, and Lo-Lo Tint 97N.However, the marine biocide may comprise any single component listed orcombinations thereof. The marine biocide may also include otherconventional biocide components, preferably in powder form, that canbond with the polymer.

The marine biocide may be supplied in a micro-sized form, wherein theaverage particle size is from about 40 μm to about 60 μm, or anano-sized form, wherein the average particle size is from about 25 nmto about 35 nm. As noted above, the biocide can continue to exist as aplurality of discrete particles dispersed within the polymer matrix onceformed into the coating composition.

The preservative may comprise VANCIDE® 89, by R. T. Vanderbilt Company,Incorporated of Norwalk, Conn. The preservative is generally included toprotect the polymer from degradation and breakdown due to bacterialgrowth. The preservative may also include other preservative componentsthat can be supplied in a powder form and can bond with the polymer.

Generally, the preservative may be provided in a micro-sized form,wherein the average particle size is from about 20 μm to about 80 μm, ora nano-sized form, wherein the average particle size is from about 25 nmto about 40 nm.

In various embodiments, the antifoulant coating may also include anantimicrobial agent, such as IRGAGUARD® (triclosan) or IRGAROL® by Cibaof Tarrytown, N.Y., indium oxide or indium-tin oxide by IndiumCorporation of Utica, N.Y., and NANOKLEAN™ by Envont Technologies ofChesterfield Township, Mich. The antimicrobial agent may be included toprovide additional protection against microbial growth that could causestaining or degradation of the antifoulant coating or that could lead tothe growth of larger organisms. Typically, as the level of theantimicrobial is increased, the level of the preservative is decreased.Thus, there is a tradeoff between additional prevention of foulantgrowth and preservation of the polymer. The antimicrobial may be addeddepending on the characteristics of the water in which the vessel isanticipated to reside primarily. Furthermore, the antimicrobial agent isgenerally provided in a blendable powder form and is capable of bondingwith the polymer.

It is possible that one or more of the polymer, the marine biocide, thepreservative, and optionally the antimicrobial agent may present a netpositive or negative electrical charge in order to aid with bonding ofthe components. It is also possible that the above components maypresent polar regions as opposed to a full charge.

In various embodiments, the antifoulant coating comprises from about 40%to about 70% by weight of the polymer, from about 37% to about 55% byweight of the marine biocide, and from about 2% to about 12% by weightof the preservative. When present, the antimicrobial agent is present ata level of from about 2% to about 8% by weight. Also when present, theadditive fluoropolymer or silicone powder is present at a level of fromabout 10% to about 20% by weight. These components are generallysupplied in a powder form with a particle sizes as described above. Thepolymer, the marine biocide, the preservative, and optionally theantimicrobial agent and fluoropolymer or silicone powder are mixed in ablender to yield a uniform powder material. The blender may be cooled toprevent overheating and coagulation of the mixture.

An exemplary mixture is created as follows. The polymer componentcomprises 47.5 pounds of polar polyamide nylon that has beenprecipitated in the form of round-shaped particles (50 micron particlesize). The marine biocide component comprises 52.5 pounds of red cuprousoxide 97N premium grade (50 micron particle size), and the preservativecomponent comprises 6 pounds of Vancide® 89 (50 micron particle size).The above components are placed in a water jacket-cooled Henschelblender and mixed at 3600 rpm for two minutes.

Next, the mixture is heated to a temperature sufficient to exceed theglass transition temperature of the polymer, and perhaps even themelting point of the polymer, but not great enough to melt the othercomponents. Generally, the mixture is heated to between about 220° F.and about 275° F. Thus, the polymer becomes flowable and can bond withthe other components. Generally, the biocide and preservative do notbond with each other, but instead are dispersed within the polymermatrix. In certain embodiments, the components comprising theantifoulant coating form bonds with each other to produce a three-partstructure, and in embodiments also comprising an antimicrobial agent, afour-part structure. In each instance, the biocide, preservative, andoptional antimicrobial agent bond or interact directly with the polymeras opposed to each other.

The mixture may also be exposed to a variable electric field in whichthe components may have their radial velocity adjusted, be separated,reoriented, or otherwise manipulated in order to maximize the percentageof material that forms a three-part (or four-part) bonded structure. Thevariable electric field is generally applied to a confined space, suchas a chamber through which the material passes, so that the motion ofthe components may be precisely controlled. For example, the electricfield may be applied to the chamber so that the polymer is physicallyaligned in the proper orientation with the marine biocide, thepreservative, and, optionally the antimicrobial to form the three orfour-part bonded structure.

Once the mixture is heated, the coating is injected into a plasma streamthat is surrounded by a shielding gas to prevent contamination of thecoating during transport to the target surface. The temperature of thecoating must be maintained at or above the glass transition temperatureof the polymer until the coating impacts the target surface (i.e., aportion of the surface of a marine vessel). However, if the coatingbecomes too warm, the bonds between the polymer and the other componentsmay break thereby leading to the decomposition of the coating. Excessivetemperatures may also lead to the formation of bonds between the marinebiocide, the preservative, and/or the antimicrobial thereby minimizingthe effectiveness of the coating to prevent foulant growth. Further, ifthe coating cools before impacting the surface, its ability to adhere tothe surface may be adversely affected. The coating may not evenly adhereto the surface thereby decreasing the lifetime of the coating.

In various embodiments, the coating may be applied to a primer coatingcomprising only the polymer if the target surface has some chemical orphysical characteristics or possibly contaminants that may affect theadherence of the coating. A polymer primer coat generally increases theadherence of the antifoulant coating to the target surface.

In various embodiments, the resulting mixture is applied to a targetsurface using a high-velocity impact fusion plasma spray gun apparatus,such as the one disclosed in U.S. patent application Ser. No.11/758,991, filed Jun. 6, 2007, which is herein incorporated byreference. For use with the plasma spray gun apparatus, the mixture isplaced into a bin or hopper that is capable of supplying the mixture ina pressurized form to the spray gun, wherein the mixture is transformedinto the antifoulant coating that is ready to be applied to a surface.

An exemplary copper-containing coating was tested following theprocedure of ASTM International (formerly American Society of Testingand Materials) standard number D6442-05 “Standard Test Method forDetermination of Copper Release Rate From Antifouling Coatings inSubstitute Ocean Water” over the course of 90 days. Essentially, thetest method determines the rate at which copper is released from anantifouling coating in substitute ocean water.

Three samples were prepared and tested using the following procedure. Acylinder approximately 2.5 inches in diameter and 7.125 inches inlength, that is designed for the purpose of testing coatings, was coatedon the lower portion of the outside of the cylinder with a polymer baseor primer comprising nylon 12. The base coat was approximately 0.005inches to 0.008 inches in thickness and was applied at approximately225° F. using a plasma spray gun. Next, a coating composition wasprepared and applied to the test cylinder on top of the polymer basecoat. The coating comprised 48% by weight nylon 12, 48% by weight purplecuprous oxide, and 4% by weight VANCIDE® 89 (captan). The coating wasapproximately 0.008 inches to 0.010 inches in thickness and was appliedat approximately 240° F. using a plasma spray gun. Two glass cylindersand one carbon fiber cylinder were prepared in this way to create thetest samples.

The test cylinder samples were tested in compliance with ASTM StandardTest Method D 6442-05 including the procedural guidelines for pH,salinity and temperature. The synthetic sea water was prepared accordingto ASTM D 1141-98, Section 6, and stored in two 100-L tanks (food-gradepolyolefin) at 25±1° C. One tank was the sample holding tank and theother tank was the sea water supply tank. The synthetic sea water wascontinually pumped at 2 to 8 turnovers per hour through the tanks. Thewater was also passed through activated carbon filters and chelatingresin filters to remove possible contaminants. The chelating resin wasre-generated if copper levels neared or were found to exceed 100 μg/L.

The synthetic sea water was analyzed in the supply and sample holdingtanks to monitor temperature, pH, and salinity within the rangesrequired by ASTM D 6442-05. The temperature was maintained between 24°C. to 26° C. The pH was maintained between 7.9 to 8.1 using NaOH or HClas necessary. The salinity was maintained between 33 to 34 parts perthousand (as measured by a conductivity meter) by adding distilledwater. The water was analyzed in the supply and sample holding tanks ateach measurement interval to maintain copper content below 100 μg/L, asrequired by ASTM D 6442-05.

The test cylinders were removed from the holding tank on days 1, 3, 7,10, 14, 21, 24, 28, 31, 35, 38, 42, 45, 49, 56, 63, 70, 77, 84 and 90and exposed to 1500 mL of synthetic sea water at 25±1° C. The testcylinders were rotated in the sampling container at 60±5 rpm for 60minutes. After the rotation period, 50 mL of the exposed syntheticseawater sample was placed in a plastic sample tube containing 50 μL ofconcentrated nitric acid and allowed to sit at least 10 minutes withoccasional shaking. The synthetic seawater sample was filtered through a0.45-μm nylon syringe filter into a plastic sample tube. Each tube wassealed in a bottle with a polyseal cap and refrigerated, as necessary,until extracted and analyzed.

The test cylinders were placed back in the holding tank of synthetic seawater until the next analysis interval. The sampling containers andlaboratory glassware were thoroughly washed in deionized water anddilute HCl before reuse.

Copper standards were prepared and used to show linearity of the methodover the range of interest and to determine the limit of detection ofthe method. A 50 mg/L standard was prepared by pipetting 5 mL of the1000-mg/L copper standard into a 100-mL volumetric flask, adding 0.2 mLof HNO₃, and diluting to volume with deionized water. A 1000 μg/Lstandard was prepared by pipetting 4 mL of the 50 mg/L solution intoanother 200-mL volumetric flask, adding 0.2 mL of HNO₃, and diluting tovolume with deionized water. A 50 μg/L standard was prepared bypipetting 5 mL of the 1000 μg/L standard into a 100-mL volumetric flaskand diluted to volume with 10% HNO₃. Similar techniques were applied tocreate standards in the range from 0 μg/L to 70 μg/L.

Spikes in artificial sea water were prepared at a concentration similarto the test cylinder samples being extracted by pipetting 1, 5 and 20 mLof the 50-mg/L stock standard solution into separate 100-mL volumetricflasks, adding 0.1 mL of high-purity HNO₃, and diluted to volume withartificial sea water to 10 μg/L, 50 μg/L, and 200 μg/L, respectively.

Solid Phase Extraction (SPE) columns, which contained Chelex 100 resin,for each test sample were rinsed with 5 mL of deionized water. Anappropriate volume of each test sample was added to produce a finalconcentration of copper between 0 and 100 μg/L. The dilution factor ofthis process equaled 10 mL divided by the sample volume. The sampleswere eluted twice with approximately 4.5 mL of 10% HNO₃ into 10-mLvolumetric flasks. The flasks were removed and diluted to volume with10% HNO₃.

The standards, spikes, a set of blank samples, and test samples wereanalyzed on a Varian 220 FS AA using a temperature and ramp sequencewhich included sample drying, ashing, atomization and tube clean-out,along with the typical AA operating conditions, shown in Table 1.

TABLE 1 Mode Graphite furnace Wavelength 324.8 nm Slit 0.5 nm SignalProcessing Peak area Replicates 3 Lamp Current 4.0 mA BackgroundCorrection D2 Sample Volume 10 μL Matrix Modifier 10 μL ofpalladium/magnesium

A blank sample and a 50-μg/L copper standard were analyzed before eachtest sample and the analysis results were used for calculating copperconcentrations. The concentrations of copper were calculated usingEquation 1:

$\begin{matrix}{C = \frac{\begin{matrix}( {{Area}_{{test}\mspace{14mu}{sample}}\; - {Area}_{blank}} ) \\{( {Concentration}_{standard} )( {{Dilution}\mspace{14mu}{Factor}} )}\end{matrix}}{( {{Area}_{standard} - {Area}_{blank}} )}} & {{EQ}.\mspace{14mu} 1}\end{matrix}$where C is the copper concentration of the test sample, given in μg/L,and the Dilution Factor is calculated as discussed above.

The release rate for each test cylinder sample was calculated using theEquation 2:

$\begin{matrix}{R = \frac{C \times V \times D}{T \times A}} & {{EQ}.\mspace{14mu} 2}\end{matrix}$where R is the copper release rate, C is the concentration of copper ascalculated in EQ. 1, V is the volume of the synthetic sea water in themeasuring tank, D is the time, in hours, per day, T is the time, inhours, of the spin during sampling, and A is the area of the testcylinder sample coating. The volume, V, was a constant 1.5 L throughoutthe test. The time, D, was a constant 24 hours throughout the test. Thearea, A, was a constant 200 cm² throughout the test. The units of therelease rate, R, are micrograms per square centimeter per day(μg/cm²/day) which is a measure of the release of the mass of copperreleased per the area of the copper-based coating per day. The testresults data for the coating 10 for the 90-day period is listed in Table2.

TABLE 2 Study No. 3670-01: Summary of Results Sample Day Day Day Day DayDay Day Day Day Day Day Day Point: Day 1 Day 7 14 21 28 35 42 49 56 6370 77 84 90 Area of 200 200 200 200 200 200 200 200 200 200 200 200 200200 Paint (cm²): Spin 1 1 1 1 1 1 1 1 1 1 1 1 1 1 Time (hours): C 37.513.7 2.6 2.2 1 2 0.8 0.8 0.7 1 1.4 0.5 0.5 0.4 (μg/cm²/ day) H 35.7 8.32.1 1.5 0.8 0.9 0.7 0.6 0.6 0.5 0.6 0.5 0.3 0.3 (μg/cm²/ day) J 42.6 144.1 1.9 1.1 1 0.7 1.1 0.8 0.6 0.5 0.5 0.5 0.3 (μg/cm²/ day) Avg. 38.6 122.9 1.9 1 1.3 0.7 0.8 0.7 0.7 0.8 0.5 0.4 0.3 (μg/cm²/ day)

The entries in column 1 of Table 2 list a portion of the data that wasrecorded for the test. The entries include the sample point, which isthe relative day on which data was recorded; the area of paint, which,for this test, is the area of the coating on the sample surface; and thespin time in hours. The next three rows are the calculated releaserates, R, (from EQ. 2) for the three different samples—one carbon fibercylinder, C, and two glass cylinder samples, H, J. The final row of thetable is the average release rate of copper from the three samples withcoating applied to them. The coating had an average release rate of 0.9μg/cm²/day for the period between day 21 and day 90, and by day 90 ofthe test, the coating had an average copper release rate of 0.3μg/cm²/day.

Thus, in certain embodiments according to the present invention, thecoating has an average copper release rate of less than about 0.3micrograms per square centimeter per day after 90 days as determined byASTM D 6442-05. It will be appreciated that other metal-containingbiocides may be used in lieu of the copper oxide. As not above,silver-containing biocides are also suitable for use with the presentinvention. In this case, the release (leach) rate of silver ions (orwhichever metal ions are present in the biocide) from the coatingcomposition is also on the order of less than about 0.3 micrograms persquare centimeter per day after 90 days.

Although the invention has been described with reference to thepreferred embodiment illustrated in the attached drawing figures, it isnoted that equivalents may be employed and substitutions made hereinwithout departing from the scope of the invention as recited in theclaims.

1. A method of applying a marine antifoulant coating to a surface of amarine vessel, said method comprising the steps of: a) applying a localvariable electric field to a heated blended mixture comprising apolymer, a marine biocide, and a preservative in a confined space and ofa sufficient strength to alter the orientation of said polymer, saidbiocide, and said preservative relative to each other; b) injecting saidheated blended mixture into a plasma stream after said local variableelectric field has been applied; c) enshrouding said plasma stream andheated blended mixture with a shielding gas to prevent contamination ofsaid heated blended mixture; and d) directing said plasma stream andsaid heated blended mixture onto said marine vessel surface, wherebysaid heated blended mixture becomes adhered to said surface.
 2. Themethod of claim 1, wherein said heated blended mixture comprises betweenabout 40% to about 70% by weight of said polymer, between about 37% toabout 52% by weight of said marine biocide, and between about 2% toabout 12% by weight of said preservative.
 3. The method of claim 1,wherein said variable electric field is applied to a chamber throughwhich the mixture passes.
 4. A method of forming and applying a marineantifoulant coating, the method comprising the steps of: a) forming ablended mixture comprising particles of a polymer, a marine biocide, anda preservative; b) heating said blended mixture to a temperature abovethe glass transition temperature of said polymer thereby forming aheated blended mixture comprising said polymer having particles of saidbiocide and preservative dispersed therein; c) applying a local variableelectric field to said heated blended mixture in a chamber through whichsaid heated blended mixture passes and of a sufficient strength to alterthe orientation of said polymer particles and said particles of biocideand preservative relative to each other; d) injecting said heatedblended mixture into a plasma stream after said local variable electricfield has been applied; e) enshrouding said plasma stream and heatedblended mixture with a shielding gas to prevent contamination of saidheated blended mixture; and f) directing said plasma stream and saidheated blended mixture onto a marine vessel surface, whereby said heatedblended mixture becomes adhered to said surface.
 5. A method of formingand applying a marine antifoulant coating using a plasma spray gunapparatus, the method comprising the steps of: a) forming a blendedmixture comprising particles of a polymer, a marine biocide, and apreservative; b) heating said blended mixture within said plasma spraygun apparatus to a temperature above the glass transition temperature ofsaid polymer thereby forming a heated blended mixture comprising saidpolymer having particles of said biocide and preservative dispersedtherein; c) applying a local variable electric field to said heatedblended mixture in a chamber within said plasma spray gun apparatusthrough which said heated blended mixture passes and of a sufficientstrength to alter the orientation of said polymer particles and saidparticles of biocide and preservative relative to each other; d)injecting said heated blended mixture into a plasma stream within saidplasma spray gun apparatus after said local variable electric field hasbeen applied; e) enshrouding said plasma stream and heated blendedmixture with a shielding gas to prevent contamination of said heatedblended mixture as said heated blended mixture exits said plasma spraygun; and f) directing said plasma stream and said heated blended mixtureonto a marine vessel surface, whereby said heated blended mixturebecomes adhered to said surface.